Device to inject solid material into a bath of liquid metal, and corresponding method

ABSTRACT

Device and method for injecting solid material in particles, powder or granulated form, of varying grain size. The device comprises a tubular pipe which can be applied on a lateral wall of a melting furnace so as to dispose its exit end inside the volume of the melting furnace and above the meniscus of the liquid metal. The device also comprises a chamber or tank to contain the solid material and emitter means comprising valve means which can be selectively opened for an opening time in the range of tenths of a second, to introduce an impulsive jet of pre-compressed gas or air which, in coordination with the opening of an exit valve which can be selectively opened, disposed at one end of said pipe, determines the emission of an impulsive flow of the solid material contained in said chamber or tank, with high kinetic energy and quantity of motion.

FIELD OF THE INVENTION

The present invention concerns a device, and the corresponding method,to inject solid material under the bath, mostly in granular form, powderand/or particles, in order to minimize the time taken for the materialto pass from the device to the bath, thus increasing the volume (weight)of the material introduced, so as to increase efficiency and generateappropriate and desired chemical reactions in a bath of liquid metal, orto add additives to the liquid metal to improve its quality, or forother reasons.

The present invention is mainly although not exclusively applied inprocesses for melting metals in electric arc furnaces (EAF) in order toimprove the efficiency of such processes, to improve the quality of theproduct obtained, to reduce melting times, to increase the working lifeof the components that are subject to wear, to increase the energyefficiency of the solids introduced, given the same volume and/orefficiency, to reduce the volumes introduced and hence the consumptionthereof, with a reduction in the purchasing costs, to reduce energyconsumption, and to obtain other advantages as described hereafter.

BACKGROUND OF THE INVENTION

Melting processes are known, which use electric arc furnaces to meltmetal materials of various types and origin, and to obtain liquid metalto be sent to working processes downstream, such as for example casting,rolling or other.

It is known that, during the melting process, as well as providingelectric energy to feed the electrodes, auxiliary devices are normallyused which perform various functions which are complementary butextremely important to optimize the process and to obtain a good qualityfinal product.

For example it is known to use burners, oxygen lances and solid materialinjectors, of varying types and function, to improve the processconditions, reduce energy consumption, and limit wear on the parts, inparticular the ends of the electrodes, forming foamy slag, and therefractory material that constitutes the hearth and parts of the lateralwalls.

For example it is known to inject or introduce carbonaceous materialinto the bath of liquid metal, in powder or particles, in order topromote the formation of foamy slag on the surface of the bath, so as toincrease the cover factor of the electric arc and thus to reduce bothwear on the electrodes and also energy consumption.

In order to perform this function, the carbonaceous material can beintroduced into the bath together with the metal material to be melted,for example mixed with it both in the case of a continuous charge with atransporter, and also in the case of an intermittent charge withbaskets.

Alternatively, or in combination, the carbonaceous material can beinjected into the bath by means of suitable lances disposed above, oreven below, the upper level of the bath of liquid metal (meniscus), soas to mix with the bath and allow to achieve chemical reactions thatpromote the rapid development of the foamy slag.

Examples of such solutions can be found in U.S. Pat. No. 6,614,831 andU.S. Pat. No. 4,110,107.

Other examples of injectors known in the state of the art are shown inDE-C-927.113, U.S. Pat. No. 3,199,924, U.S. Pat. No. 3,239,278 andGB-A-792.192.

DE'113 describes an injector to inject solid material into a furnace,which is mounted horizontally on the wall and, substantially near itsterminal end and outside the furnace, has a magnet that regulates thequantity of material to be injected. This solution in no way allows toobtain an injection deep into the bath, keeping the injector outside andabove the bath. Moreover, with the regulation methods using the magnet,it is not possible to obtain the emission speeds and energies requiredto obtain an injection of the carbonaceous material deep into the bathof liquid metal.

US'924 describes an injector to inject solid material through a thinchannel made on the wall of the furnace, which leads into the bath ofmetal. The injection of the solid material directly inside the bath doesnot allow to obtain an in-depth distribution and determines a loss ofefficiency and a delay in the effect of the solid particles in the bath.Furthermore, to prevent the material of the bath from rising inside thechannel in the wall of the furnace and into the injector, the pressurein the chamber used for loading the carbonaceous material must be higherthan the pressure in the furnace, and this causes operational andmanagement complications.

US'278 also has a solution similar to US'924, with an injector insertedinto the furnace wall that leads out directly inside the bath of liquidmetal, with the same disadvantages as described above.

GB'192 does not show an injector suitable to be applied to the wall ofan electric furnace for melting metal, but shows a tank of solidmaterial from which an adjustable quantity of material is extracted.

It must also be considered that none of the documents described aboveteaches to use a flow of air or other gas under pressure, delivered inan impulsive manner (that is, with extremely limited emission times,high speed and high energy) to inject sold material from above themeniscus into deep into the bath.

It has been seen that the known methods described above for theintroduction of carbonaceous material, and in general other solidmaterials inside the bath of liquid metal, are not satisfactory from theperspective of increasing the energy efficiency of the solids introducedand optimization of the results sought.

Indeed it has been found that, where the injector is above or inside thebath, the efficiency of the process is limited because the carbonaceouspowders or particles affect only the upper layer, or in any case alimited layer, of the bath of liquid metal, and only later do theyaffect the remaining part.

In these cases, the delayed and limited start of the chemical reactionsbetween the carbonaceous material and the bath of liquid metal causesthe foamy slag to form late, and therefore the effect of covering thearc is contained, and hence the function of preserving the electrodesfrom wear is not performed efficiently, nor are energy savings achieved.

Another disadvantage is that this type of introduction promotes a lossof the product, which burns and goes into the fumes, without anyadvantage whatsoever for the process.

One purpose of the present invention is therefore to increase theefficiency of introducing the solid material, mostly in granular, powderand/or particle form, inside a bath of liquid metal in a meltingprocess, in order to maximize the volume or weight of materialintroduced into the bath and the depth into the same, with the advantagethat when it is under the bath it reacts with maximum yield.

Another purpose is to accelerate the start of the chemical reactions,involving all the liquid metal of the bath so as to maximize the finalresult of said reactions.

The Applicant has devised, tested and embodied the present invention toovercome the shortcomings of the state of the art and to obtain theseand other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independentclaims, while the dependent claims describe other characteristics of theinvention or variants to the main inventive idea.

According to the present invention, an injection device is provided withhigh kinetic energy and high quantity of motion, to inject a discreteamount of solid material in particles, powder or granulated form, ofvarying grain size, for example comprised between 0.15 and 15-20 mm,preferably between 5 and 8 mm. The injection device comprises a tubularpipe which can be applied on a lateral wall of a melting furnace so asto dispose its exit end inside the volume of the melting furnace, with adesired orientation with respect to the vertical, for example comprisedbetween 15 and 70 degrees, above the meniscus of the liquid metalcontained in the melting furnace.

The injection device is suitable to inject a predetermined amount ofsolid material inside the bath of liquid metal, substantially of anytype in relation to the result to be obtained, for example carbonaceousmaterial, slag formers such as for example lime, inert materials, slag,materials from demolitions, for example fluff from shredders, powdersfrom fume sleeve filters, minerals of different types, etc.

According to the present invention, upstream of the tubular pipe andassociated with it, the injection device comprises a chamber or tank tocontain the solid material, and emitter means able to be selectivelyconnected to the chamber or tank, and configured and suitable to producean impulsive jet of pre-compressed gaseous fluid which, in combinationwith an exit valve that can be selectively opened, disposed at one endof the pipe, determines the emission of an impulsive flow of thematerial contained in the chamber or tank, with high kinetic energy andhigh quantity of motion, such as to substantially reach the bottom ofthe hearth, passing through the whole layer of slag and the bath ofliquid metal.

In a preferred solution, the impulsive jet of fluid consists of a highpressure gas that is introduced, making it expand, inside the chamber ortank containing the solid material, in a position upstream of the exitvalve, in temporal coordination with the opening of the valve.

By doing this, that is, by substantially synchronizing the introductionof the pressurized fluid, for example gas or air, inside the device andthe opening of the exit valve, and using extremely limited opening timesboth of the valve that introduces the pressurized gas inside the devicewhere it expands, and also the exit valve of the material from thedevice, a flow of material is obtained with high kinetic energy and highquantity of motion, which penetrates and passes through the layer ofslag and liquid metal and substantially reaches the bottom of thehearth.

In a preferential form of embodiment of the invention, a speed tointroduce the material is used which is more than 4 m/s, advantageouslymore than 8 m/s, even more preferably more than 9-10 m/s.

In another preferential form of embodiment of the invention, the openingtime of the valve which introduces the pressurized gas or air inside thetubular pipe of the device is less than 0.4 seconds, advantageously lessthan 0.3 seconds and even more advantageously less than 0.2 seconds.

In a preferential form of embodiment, the pressure of the gas introducedinto the tubular pipe of the device to achieve the emission of theimpulsive flow of material is higher than 5 bar, advantageously higherthan 7 bar, even more advantageously higher than 8-10 bar.

The flow rate of material emitted with every impulsive emission cycle,in a preferential solution of the invention, is advantageously higherthan 2 kg/s, more advantageously higher than 3 kg/s, even moreadvantageously higher than 4-5 kg/s.

In another preferential solution, the opening time of the exit valve ofthe material, associated with the end of the tubular pipe of the device,is comprised between 0.2 and 0.8 seconds, advantageously between 0.3 and0.7 seconds, and even more advantageously between 0.4 and 0.6 seconds.

According to the invention, the values indicated above can be modifiedaccording to the operating conditions and the result to be obtained.

For example, the values can be modified according to the height of theliquid bath into which the material is injected, which can varyaccording to the melting cycle under way. During and at the end of thetapping step, for example, the level of the liquid bath inside thefurnace is very low, in the range of 200-400 mm, corresponding to theheight of the “hot heel” that is always maintained inside the furnace.

This situation, that is, the introduction of carbonaceous material atthe end of tapping, is very important for the optimization of theprocess in that it is necessary that, when the new melting cycle starts,a foamy slag is obtained with a height and volume such as to guaranteethe adequate cover of the electric arc and the material of the furnacethat is subject to wear.

In this situation, the introduction parameters, mainly speed of flow,delivery rate and opening times of the valves, will be suitablycalibrated in order to ensure that the bottom of the hearth is reachedwithout ruining it by part of the jet of materials, and that the latterare distributed to affect the whole liquid bath.

If solid material is introduced during the melting process and/or duringrefining, when the level of the bath can reach 800-1000 mm or more, theintroduction parameters will be increased compared to the previous caseconcerning the post-tapping step, achieving the same advantages that thepresent invention allows to obtain.

The geometric parameters of the device, for example length and diameterof the tubular pipe, distance of the exit end from the upper level ofthe bath, angle with respect to the vertical, etc., can also be modifiedboth during the initial assembly step and also during the introductionof the material into the bath.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will becomeapparent from the following description of a preferential form ofembodiment, given as a non-restrictive example with reference to theattached drawings wherein:

FIG. 1 shows a device according to the present invention applied on awall of an electric furnace;

FIG. 2 is a plan view of an electric furnace where an injection deviceaccording to FIG. 1 is applied;

FIG. 3 shows a device according to the present invention in a variant ofFIG. 1.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF EMBODIMENT

With reference to the attached FIGS. 1 and 2, the reference number 10denotes in its entirety a device to inject solid material in granularform, powder or particles, able to be applied to a panel thatconstitutes part of the lateral wall of an electric furnace 11, in thecase shown here the electric type (EAF).

The electric furnace 11, during use, contains a bath of liquid metal 12with an upper surface 12 a that can have a variable height, normallyfrom a minimum of about 200-400 mm, usually corresponding to the “hotheel” that always remains inside the furnace, even after tapping, to amaximum of about 800-1000 mm, during the completion of the melting stepand refining.

The liquid metal 12 can be covered by a layer of slag 13 normally havinga height of about 200-500 mm when inactive.

The furnace 11 comprises a hearth 14 made of refractory material, whichdefines the bottom of the hearth 14 and lower part of the lateral walls,above which cooling panels 15 are disposed. The whole thing is closed bya roof (not shown) through which the electrodes (also not shown) areinserted: all this is substantially known in the state of the art.

The device 10 is applied in cooperation with the cooling panels 15 andsubstantially comprises a tubular pipe 16, having a diameter that canvary between 60 and 150-200 mm, advantageously between 80 and 120 mm,and a length that can vary between 800 and 1500 mm.

In the case shown as an example in FIG. 2, there is a single device 10applied on a respective panel 15, but it is clear that in some forms ofembodiment there may be more than one injection device, disposed on thecircumference at the proper technological distances from each other.

A lower end 16 a of the tubular pipe 16 is inside the electric furnace11, facing toward the liquid metal 12 for the injection of the solidmaterial, and disposed during use above the level of the upper layer ofslag 13, and an upper end 16 b of the tubular pipe 16 is associated,that is, rigidly fixed, to a first exit valve 17, and in axis with thelatter.

The first exit valve 17 selectively connects the tubular pipe 16 withthe lower end of a chamber or tank 18, able to contain a predeterminedand discrete quantity of material.

The tank 18 is elongated in shape and substantially aligned axially withthe tubular pipe 16.

In the form of embodiment shown in FIGS. 1 and 2, a second valve 19 isassociated with the upper end of the tank 18. Upstream, a pipe 20 isassociated with the second valve 19, usable to feed the solid materialin granules, powder or particles into the tank 18.

The pipe 20 can be any type, and is connected to an accumulation tank,an automatic feed line or other apparatus to store and feed the solidmaterial in powder or granular form of the type in question.

The pipe 20 can also be associated to deflector mechanisms and/ormulti-way valves for connection to a plurality of tanks, each containinga material of a different type and grain size according to the type ofprocessing and/or the processing step in progress.

A pipe 21 to introduce a pre-compressed fluid, in this case pressurizedgas, for example air or preferably another, substantially inert gas, isprovided in association with the device 10: the connection or couplingposition of the introduction pipe 21 is provided advantageously incorrespondence with the upper part of the tank 18.

A valve 22, or third valve, is provided along the pipe 21 in order toactivate/de-activate the introduction of the pre-compressed gas upstreamof the tank 18, thus generating, in coordination with the opening of thefirst valve or exit valve 17, the emission of an impulsive flow ofmaterial, indicated in FIG. 2 by the letter F, under the thrust of thepre-compressed jet of gas, which expands, toward the liquid metal 12.

In a coordinated manner, the tank has a zone 18 a of selectivecommunication, thanks to the third valve 22, with the pipe 21, that is,a zone 18 a of the tank 18, in correspondence with the coupling of thepipe 21, where the pre-compressed gas enters, expanding, into the tank18: for the functioning of the device 10 the zone 18 a must preferablyremain free of material.

The procedure for filling the tank 18 provides to close the first exitvalve 17, or exit valve, to open the second valve 19, or entrance valve,and to activate a mechanism to feed the material (not shown, andgenerally known) through the pipe 20. Once the tank 18 has been filledwith the desired quantity of material, the second valve 19 is closed andthe device 10 is ready for the introduction of the material inside theliquid bath when the valves 17 and 22 are subsequently opened. Inparticular, the material is introduced toward the liquid metal 12 byopening the first exit valve 17 and then, in rapid sequence, the thirdvalve 22, to allow the impulsive jet of pre-compressed gas to expandinside the tank 18. The impulsive jet of pre-compressed gas is mixedsubstantially instantaneously with the solid material in the tank 18 anddraws it through the tubular pipe 16, obtaining the emission of theimpulsive flow F of material contained in the tank 18 with high kineticenergy and high quantity of motion through the tubular pipe 16 towardthe liquid metal 12.

Depending on the type of material, the processing conditions, the resultto be obtained, the quantity of liquid metal 12 inside the furnace 11,the position and structure of the device 10, the operating parameters ofthe device 10 can be regulated and varied to obtain the bestfunctionality, even during the course of the introduction step itself.

The present parameters, preferential but not binding or restrictive,were tested by Applicant for a procedure to introduce carbonaceousmaterial used to activate the formation of foamy slag in a step aftertapping a quantity of liquid metal from the furnace 10.

To obtain an introduction speed of the material higher than 9-10 m/s,which has proved itself to be advantageous to allow the material toreach the bottom of the hearth 14 and allow an effective propagation ofthe material to a great quantity of metal, the third valve 22 was openedfor a time of less than 0.2 seconds.

The pressure of the pre-compressed gas introduced from the pipe 21inside the tubular pipe 16 of the device 10 to achieve the emission ofthe impulsive flow F of material was higher than 8 bar.

The flow rate of material emitted with every impulsive cycle was higherthan 4.5 kg/s, while the first exit valve 17 for the material was openedfor between 0.4 and 0.6 seconds. The overall cycle for the impulsiveflow F of material was less than 1 second.

The flow rate of material injected into the liquid bath was about 5-6kg/s, while the flow rate of the pressurized gas was about 40-70 l/s.

Using these values, with an average grain size of the carbonaceousmaterial about 2-4 mm, the time taken to pass through the whole heightof the liquid bath was about 0.1 sec, thus obtaining the result that allthe carbonaceous material passed through the layer of slag 13 above andthe whole thickness of liquid metal 12 without dispersing or creatingflashes or other losses during the passage.

In this way, an extremely high percentage of the carbonaceous materialinjected was able to react substantially immediately with the liquidmetal 12, quickly creating the conditions for the formation of a largevolume of foamy slag, giving advantages to the processing conditions forre-starting a new casting cycle.

The above parameters can be modified in the case of different materials,and/or different processing conditions, but shall in any case comewithin the ranges indicated in the present description.

FIG. 3 shows another form of embodiment of an injection device 110. Inthis figure, the same numbers are used to refer to components identicalor corresponding to those shown in FIG. 1.

The device 110 shown in FIG. 3 does not have the second introductionvalve 19 to delivery the material, and the solid carbonaceous materialis accumulated in the tank 18, upstream of the pipe 16, directly throughthe pipe 20 connected to an external silo (not shown), at a relativelylow constant pressure, for example in the range of 1-2 bar. When thetank 18 is full, the device 110 is ready for the injection, at highspeed and high energy.

When the valve 22 for the air or other gas is opened and theintroduction of the pressurized gas is activated and, in coordination,the exit valve 17 is opened, in the way and with the times as describedabove, the material in the tank 18 is shot through the pipe 16 into theliquid metal 12 at extremely high speed to obtain a high penetratingenergy. As already described, the pressure used for the expulsion ismore than 5 bar, advantageously more than 7 bar, even moreadvantageously more than 8-10 bar, and is therefore much higher than thepressure at which the material is introduced inside the tank 18; thanksto the difference between these two pressures, during the expulsion, theintroduction of material into the tank 18 is blocked. When theintroduction of the gas is finished, the tank 18 is automaticallyrefilled and is ready for a new cycle to introduce material into thebath.

This variant allows to obtain a smaller device than the device in FIG.1, therefore having less weight, so as to be moved manually, withouthaving recourse to cranes or other devices for mechanical movement.

It is clear that modifications and/or additions of parts may be made tothe device as described heretofore, without departing from the field andscope of the present invention.

1.-13. (canceled)
 14. An injection device for injecting a discreteamount of solid material in particle, powder or granulated form,comprising: a melting furnace having walls defining a liquid metalretaining area, a first pipe having a lower end, an upper end andmounted through a lateral wall of the melting furnace wherein the lowerend of the first pipe is disposed inside the furnace and configured tobe above a meniscus of liquid metal contained within the liquid metalretaining area, a chamber configured to store the solid material andhaving an upper part and a lower end, an exit valve connecting the upperend of the first pipe to a lower end of the chamber wherein the exitvalve is configured to be selectively opened for a period between about0.2 seconds and about 0.8 seconds, a second pipe connecting the upperpart of the chamber to introduce the solid material into the chamber, athird pipe connecting to the upper part of the chamber to introduce apre-compressed fluid into the chamber, a fluid valve connecting thethird pipe to the upper part of the chamber wherein the fluid valve isconfigured to be selectively opened for a period less than about 0.4seconds, wherein by rapidly and sequentially opening the exit valve andthe fluid valve, the exit valve emits an impulsive flow of the solidmaterial into the furnace.
 15. The injection device according to claim14, wherein the impulsive flow of the solid material is higher thanabout 4 m/s.
 16. The injection device according to claim 15, wherein theimpulsive flow of the solid material is higher than about 8 m/s.
 17. Theinjection device according to claim 16, wherein the impulsive flow ofthe solid material is higher than about 9-10 m/s.
 18. The injectiondevice according to claim 14, wherein the opening period of the fluidvalve is less than about 0.3 seconds.
 19. The injection device accordingto claim 18, wherein the opening period of the fluid valve is less thanabout 0.2 seconds.
 20. The method according to claim 14, wherein thepressure of the pre-compressed fluid is higher than about 5 bar.
 21. Themethod according to claim 20, wherein the pressure of the pre-compressedfluid is higher than about 7 bar.
 22. The method according to claim 21,wherein the pressure of the pre-compressed fluid is higher than about8-10 bar.
 23. The method according to claim 14, wherein the flow rate ofmaterial emitted is higher than about 2 kg/s.
 24. The method accordingto claim 23, wherein the flow rate of material emitted is higher thanabout 3 kg/s.
 25. The method according to claim 24, wherein the flowrate of material emitted is higher than about 4-5 kg/s.
 26. The methodaccording to claim 14, wherein the opening period of the exit valve isbetween about 0.3 seconds and about 0.7 seconds.
 27. The methodaccording to claim 26, wherein the opening period of the exit valve isbetween about 0.4 seconds and about 0.6 seconds.
 28. The injectiondevice according to claim 14, wherein the chamber is aligned axially tothe first pipe.
 29. The injection device according to claim 14 whereinfurther comprising an entering valve connecting the second pipe to theupper part of the chamber.
 30. The injection device according to claim14, wherein the upper part of the chamber directly connects to thesecond pipe so that the solid material is directly introduced into thechamber at a pressure between about 1 bar and about 2 bar.
 31. A methodfor injecting a discrete amount of solid material in particle, powder orgranulated form, comprising mounting a first pipe through a lateral wallof a melting furnace, wherein the melting furnace has walls defining aliquid metal retaining area, the first pipe has a lower end and an upperend, the the lower end of the first pipe is disposed inside the furnaceand configured to be above a meniscus of liquid metal contained withinthe liquid metal retaining area, connecting the upper end of the firstpipe to a lower end of a chamber via an exit valve, wherein the chamberis configured to store the solid material and has an upper part, theexit valve is configured to be selectively opened for a period betweenabout 0.2 seconds and about 0.8 seconds, connecting a second pipe to theupper part of the chamber to introduce the solid material into thechamber, connecting a third pipe to the upper part of the chamber tointroduce a pre-compressed fluid into the chamber via a fluid valve, thefluid valve is configured to be selectively opened for a period lessthan about 0.4 seconds, and by rapidly and sequentially opening the exitvalve and the fluid valve, the exit valve emits an impulsive flow of thesolid material into the furnace.
 32. The method according to claim 31wherein further comprising a filling step comprising disposing thechamber aligned axially to the first pipe, connecting the second pipe tothe upper part of the chamber via a entering valve, closing the exitvalve, opening the entering valve to feed the solid material into thechamber, and closing the entering valve when the solid material in thechamber reaches its desired amount.